ADSORPTIOS BY- hIETALLIC HYDROXIDES. 11'. ADSORPTION BY PRECIPITATED CHROMIUM HYDROXIDE BY KSHITISH CHANDRA S E N
I n the preceding papers, I have studied the adsorptive power of ferric hydroxide and aluminium hydroxide on acids. The results obtained with hydrated chromium oxide will now be given. Hydrated chromiunl oxide has not been much studied as an adsorbent. There are only a few instances in the literature where this substance has been used in adsorption experiments. Thus Wohlcr, Pluddemann and Jt'ohler' mention that chromium oxide adsorbs benzoic acid and acetic acid about equally; but practically no other instance can be found where chromium oxide has been used as an adsorbent for acids. Owing to this reason, the adsorptive power of this substance has been investigated in detail. A peculiar fact in connection with hydrated chromium oxide is that, with this substance, no true equilibrium can be obtained, the amount of adsorption gradually increasing with time. But if the time of contact is kept constant, quite reproducible values of the amounts of adsorption can be obtained. Further the adsorption equilibrium is not a reversible one. These behariours differentiate this substance from the hydrated oxides of iron and aluminium studied beforehand. I n order therefore to get some comparative results, the same length of time ( 2 0 hours) as was given in the case of aluminium and iron hydroxides, has been given, and all other conditions have been kept the same. Adsorption of Arsenious Acid I n the first instance, the adsorptive power of chromium hydroxide for arsenious acid will be given. Several samples of the hydroxide have been used, and it has been found that different samples give different values of adsorption. The hydroxide used in Table I was precipitated from chromium sulphate solution by means of excess of ammonia and freed from electrolytes partly by decantation and then by dialysis. On analysing the hydroxide after dialysis, it was however found to contain some sulphate, which could not be removed. The first experiment was made to test the reproducibility of the resqlts. TABLE I 1Vt. of Cr203 = 0.5914 gr.; time = 2 0 hours; concentration and adsorption in cc I = X/18.302 Conc.
As203
Adsorption
Conc. A s n o s
107.9
'14.9
107.9
76.6 76.6 Z.physik. Chem., 62, 664 (1908).
ildsorption
'14.9
74.6 74.6
923
ADSORPTION B Y XETALLIC HYDROXIDES
The above results show that when the time of contact is twenty hours, the amount of adsorption remains the same and quite reproducible results can be obtained in duplicate measurements. I n Table 11, the effect of time is shown. 'FABLE
11
( ' r ? 0 3 = 0.5911 gr. Original conc. of . h 0 3in grms. 0.j I j 0
.Idsorption in 2 0 hours
Adsorption in 48 hours
0.4198
0.4374
C r ? 0 3 = 0.3496 grin. 0
4556
o 2829
o
2278
0
o 2991
1954
0 2251
7 hew results sho\v that the time of contact has an iniportant effect inasmuch as the amount of adsorption increases with the increase in the duration of contact. I n Table I11 the adsorption of arsenious acid at different concentrations by a fixed amount of the hydroxide is shoRn.
111 cc.: ILCI 2 0 hours
TABLE
(lr201 =
0.5914
gr.; volume
= 100 =
Original conc. of . h O I in grams
o 5665 0.5IiO
0.4635 0.4136
0.3102 0,2068 0.1034
Conc. of solution after adsorption
o 1206 0 09715 o 0648 o 0486 0 0175 0
0054
0 0008
= 0.05
mole per litre.: time .Idsorption per gram adsorbent
0.7541 0.7099
0.6742 0.6172 0.4949 0,3405 0 I735
In Table IV, the eficct of vtrrying the amount of the adsorbent on the extent of adsorption from a constant amount of arsenious acid is shown.
TABLE IV Conc. of As203 = 0.3102 gr. A = amount of adsorbent in grams. B = concentration of solution after adsorption. C = adsorption per gram adsorbent. B C B C .I A 0.2ojz 0.8884 0.4728 0.0378 0 . jj62 0 .I I82 0.1256 0.2364 0,5914 0.7809 o.01j6 0.4949 0.6692 0.7092 0.0108 0.4223 0.3546 o.oj29 Efect of colunie when the total solute concentration is the same in all cases, Table V.
924
KSHITISH CHANDRA SEX
TABLE V Conc. of Xs203= 0.4136grams; wt. of C r 2 0 a= 0,5914gr. Volume of solution
Volume of solution
Amount of adsorption
Amount of adsorption
90 cc
0.3602 70 cc 0.3654 60 cc 0 3731 0 3629 In the following tables, a smaller amount of the adsorbing material has been used. The object was primarily to compare the adsorption isotherms obtained by using different amounts of the adsorbent. The net amount of adsorption will thus be different. The results of adsorption experiments witk. varying amounts of . A S 9 0 3 are shown in Table VI. Other conditions remain the same. 80 cc
TABLE
1-1
C r 2 0 3 = 0.3496 gr.
A
original concentration of As&3 in grams. €3 = concenLration of solution after adsorption. C = adsorption per gram adsorbent. A B c B C A 0.5696 0.2631 0.8766 0.3417 0.0917 0.715” 0.2848 0.0580 0.6486 0.1726 0.809j 0.45j6 o.zzj8 0.1322 0.7623 0.3986 0.0323 0 .jj91 =
E$ect o j volume when the total solute concentration is the same in each case, Table VII. TABLE VI1 Cr?OJ = 0.3496 gr. Conc. of . k 3 ? 0 3 = 0 . 2 2 7 8 gr. Volume of solution
.Imount of adsorption
Volume of solution
Amount of adsorption
cc 90 cc 80 cc
0 .195.5
70 CC
o
0 .‘975
60 cc
o 2060
IO0
2023
0.2009
Effect o j volume when the total amount of solute is different but the concentration in terms of normality is the same in each case, Table VIII. TAHLE VI11 Cr203= 0.3496 gr. Conc. of A s 2 0 3 = 0.2278 gr. per Volume of solution
cc 90 cc 80 cc
IO0
Adsorption in grams 0.19548
0.18079 0.16502
IOO
Volume of solution i o cc
60 cc
cc. Adsorption in grams 0 .I j006 0.131868
92s
ADSORPTION BI' METALLIC HI'DROXIDES
Effect c j IciKperature on the hydroxide. To study the effect of heat on the sample of chromium hydroxide, 0.3496 grams of the hydrated oxide was taken in flasks which were then inimerscd in boiling water for I j niinutes. l h e flasks were then cooled, and the adsorption values were measured in the usual way, Table IX. TARLE IT; A = original concentration of . A S 2 0 3 in grams. B = adsorption by oxidenot heated. C = adsorption by oxide-heated .i
B
C
0.39865 0.3417
0.26649 0.2joo2
0.23949 0.22842
c
B
A 0.284;j 0.2zj8
0.2268 0.19548
0.2138 0.18738
It will be obscrved that the adsorptive power of the heated sample is much less than that of the sample which has not been heated. I n Table X the adsorption of sodium arsenite by the same sample of hydroxide is shown. TABLE X Clr2O3 = 0.3496 gr. Concentration and adsorption in cc I ? S '18.302 Conc. Sa-arsenite
Amount adsorbed
Conc. Na-arsenite
.o
I 04 0
10;. j
168.8 126.6
97 3 8j.j
84.4
211
Amount adsorbed
78.5 68.9
In Table X I thc relative adsorbability. of sodium arsenite and arsenious acid when the initial concentration in iodine equivalents arc the same, is compared.
TABLE XI Crd.33 = 0.3496 gr. Concentration and adsorption in ccI? ?; 18.302 Originai conc. 211.0
168.8 126.6
Adsorption of .is?O,
113.5 104.8 92.6
.idsorption of Sa-Arsenite
104.0 9i.3
Original conc. 1 0 5 .j
84.4
Adsorption .idsorption of of . i s 2 0 1 Sa-.irsenitp
84.0
7s.j
72.4
68.9
85.5
I t will be observed from Table S I that arsenious acid is more ndsorbcd than sodium arsenite. This result is therefore different froni that obtained in the case of aluminium hydroxide where the amount of adsorption is the same in both cases. The hydroxide which has been used so long, as has already been stated, contained appreciable amounts of sulphate which could not br freed from i t by washing. It was therefore thought desirable to riiake some morc experinients with a sample almost free from adsorbcd impuritirs. Ilencc another
926
KSHITISH CHAXDRA S E S
sample of chroniium hydroxide was prepared from a chromic chloride solution with an excess of ammonia. This sample could be washed practically free from adsorbed chloride by continued dialysis. In Table XI1 some results on the adsorption of arsenious acid with this sample are given. Other conditions remain the same. T.4BLE
CrzOa =
A
=
0.2610
XI1
gr.; time =
hours
20
original concentration of A s ? O ~ in grams. I3 = concentration of solution after adsorption. C = adsorption pc.r gram adsorbent
A
€3
c
A
R
